1. Field of the Invention
The invention relates to an orthodontic component part, for example a bracket made of plastic, as described in the generic term of claim 1 and a method for the production of said component part.
2. The Prior Art
In a known orthodontic device--according to U.S. Pat. No. 1,976,141 and U.S. Pat. No. 2,045,025, the tooth attachments are made of stainless steel and secured to a stainless steel band which encircles the tooth to hold the tooth attachment in the appropriate position.
Various other tooth alignment methods and orthodontic devices have been developed in which stainless steel tooth attachments are cemented directly to the surface of the tooth. These methods and devices require no band to secure the tooth attachments. Such systems are often used. Inter alia, these known tooth alignment methods and devices are disclosed in U.S. Pat. Nos. 4,604,057, 4,430,061 and 4,322,206. The metallic appearance of such stainless steel tooth attachments is a significant drawback. Therefore, for reasons of appearance, in particular adult patients desire orthodontic devices, which are not made of metal but of transparent or translucent materials as such materials provide improved cosmetic appearance. Accordingly, transparent plastic materials are used, mostly polycarbonates or transparent or translucent ceramic materials of aluminum oxide. In known tooth attachments, which consist of non-metallic materials and are produced in very small sizes to keep cosmetic drawbacks at a minimum, it is known--according to U.S. Pat. No. 4,302,532 -- that the strength of ceramic tooth attachments of plastic materials is increased by reinforcing elements.
Furthermore, orthodontic devices with a ceramic tooth attachment consisting of a polycrystalline ceramic structure with various additives, are also known. A known ceramic tooth attachment--according to U.S. Pat. No. 4,954,080--consists of polycrystalline ceramics with a light transmission in the visible spectrum, which reduces the visibility of this tooth attachment, so that when it is mounted on the tooth, it can be hardly recognized by a third party. This polycrystalline ceramic body for the ceramic tooth attachment is produced by pressing powdered high purity aluminum oxide, which is then sintered to present a close to zero porosity and an average grain size in the range of 10 to 30 micrometers. Preferably, the tooth attachment should be colorless. An in-line light transmission in the visible spectrum should be 20 to 60% through a specimen having a thickness of 0.5 mm. The drawback of this tooth attachment is that it cannot be seen when X-rays are made.
However, it is already known--according to EP-B-O 189 540--that microfilled dental material is being manufactured which presents both, good X-ray opaqueness and simultaneously good transparency. This dental material which is used as filling material, dental cement, crown and bridge material, prothetic material and also for the production of dentures, inlays, implantations and prefabricated parts, consists of polymerized inorganic binders and compositions of rare precious metals and also, if required, further inorganic compositions as filling materials, whereby it may also contain a fluorinated rare earth-metal (elements of atomic number 57-71 of the periodic table of elements) or a mixture of these fluorides. This type of dental material is often mixed to a paste by kneading, which hardens under various conditions, in particular under the effect of light. The light transmission in the visible spectrum for such parts is in most cases enough, however, when used for tooth attachments and orthodontic devices it was not satisfactory.